Entire species of plants are dying off in droves, just like mammals. And there's no way to save them all, say scientists. How do you decide which plant species to preserve at all costs, and which ones to consign to oblivion forever? Answering that question may mean the difference between selective extinction for some — and worldwide extinction for all.A team from UC Santa Barbara is working on this very question, and they've just published a study in the Proceedings of the National Academy of Sciences. They believe Earth is in its sixth mass extinction, which will kill off nearly 50% of all plant and animal species. Figuring out which endangered plants to save may be the key to minimizing the ecological impact of this particular extinction:

"Losing a very unique species may be worse than losing one with a close relative in the community," said [co-author Todd] Oakley. "The more evolutionary history that is represented in a plant community, the more productive it is." [Post-doctoral fellow Marc W.] Cadotte explained that the buttercup is a very unique species, evolutionarily. Losing the buttercup, where it occurs in grasslands, would have a much bigger impact on the system than losing a daisy or a sunflower, for example. The latter species are closely related. Each could therefore help fill the niche of the other, if one were to be lost. The daisy and sunflower also have a more similar genetic make-up.